Gravity sorter and fast normalizer



Oct. 27, 1953;

Filed Dec.

D. C. COX

GRAVITY SORTER AND FAST NORMALIZEIR 5 Sheets-Sheet l INVENTOR. DAV/D C. COX

ATTORNEY D. C. COX

GRAVITY SORTER AND FAST NORMALIZER Oct. 27, 1953 5 Sheets-Sheet 2 Filed D90. 15. 1948 INVENTOR. DAV/D C. COX

Oct. 27, 1953 D. c. cox

GRAVITY SORTER AND FAST NORMALIZER 5 Sheets-Sheet 3 Filed Dec. 13. 1948 INVE1\'T0R. DAV/D C. COX

p/ezcr/o/v 0; DPAVKA Fig. 5 64 J ATTOPNF Oct. 27, 1953 D. c. cox 2,656,923

GRAVITY SORTER AND FAST NORMALIZER Filed Dec. 15. 1948 5 Sheets-Sheet 4 INVEN TOR. QAV/D C. C OX ATTORNEY Oct. 27, 1953 D. c. cox 2,656,923

GRAVITY SORTER AND FAST NORMALIZER Filed Dec. 13. 1948 5 Sheets-Sheet 5 1N VEN 'IOR.

DAV/D C. cox

A 77' OE/VE y Patented Oct. 2 7, 1953 UNITED STATES PATENT OFFICE 2,656,923 GRAVITY soltrsn AND FAST NORMALIZER fiavid C. Cox, Grand Rapids, Mich, assignor to Electric Sorting Machine Company, Grand Rapids, Mich a corporation of Michigan Application December 13, 1948, Serial No. 64,967

6 Claims. (01. 209-111) My invention relates to article sorting and to avoiding errors in operation of sensitive electronic circuits responsive to characteristics of articles being sorted.

It is an object of the invention to obtain more accurate and reliable sorting of articles which are sorted by employment of their light reflective properties.

A further object is to normalize or stabilize electronic circuits for rendering them unaffected by unavoidable changes in such circuit constants and electrical properties as tend to cause drift in the magnitude of input values which are required to produce circuit actuation.

Still another object of the invention is to anable free falling articles to be sorted without requiring that the articles be located mechanically or supported during the operation of the selective mechanism serving to sort the articles.

Another object of the invention is to obtain a response to predetermined light reflective properties of any portion of a surface of articles to be sorted and to provide a lamp housing enabling this object to be accomplished.

A further object of the invention is to enable articles such as lemons and other fruits and relatively fragile articles to be sorted automatically at a high rate of speed without bruising or otherwise damaging the articles.

Still another object of the invention is to enable amplifiers of the electronic type to operate in a manner simulating characteristics of long time constant circuits, so as to obtain very precise, sensitive, and accurate response 01 actuation as a result of minute deviation in the light reflective properties of a sorted article from a predetermined standard of comparison, while retaining characteristics simulating those of short-timeconstant circuits for enabling the circuit to be normalized or have its bias corrected very quick- 1y during the intervals between sorting operation, in order to compensate for circuit variations and drift in characteristics of various circuit elements.

Other and further objects, features and advan tages of the invention will become apparent as the description proceeds.

In carrying out the invention in accordance with a preferred form thereof, as applied to the sorting of articles such as lemons, I provide a framework supporting at the upper portion thereof, a substantially horizontal conveyor adapted to receive lemons or other articles at one end and having a sorting head mounted below the other end of the conveyor. The sorting head includes a lamp housing having a vertical passageway therein for freely falling objects with an upper gate normally closing the upper end of the passageway and a lower gate at the lower endof the passage for enabling the objects to be diverted in one direction or another, according to the response produced in the sorting mechanism. The lamp housing has side walls shaped to form a hexagonal prism and lamps mounted slightly beyond the upper and lower edges of the side walls for indirectly illuminating the interior of the lamp housing and casting diffused light upon the articles falling along the axis of the prism. Background screens or reference backgrounds are provided along three alternate vertical walls of the prism to serve as standards of comparison of the light reflective properties of the articles being sorted, and at the three remaining side walls light-receiving and directing elements are provided.

If desired, each of these light-receiving and directing elements may comprise a lens system adapted to form received light into a beam projected against a photoelectric tube. Preferably, however, two of the light-directing elements comprise mirrors mounted at such an angle as to refleet the light toward the wall containing the lens system forming the remaining light-directing element, and a single photoelectric tube is provided for response to the reflected light in all three of the beams of light. This arrangement is preferable for the sake of simplicity and minimum cost of apparatus, especially in the case of a photoelectric sorting operation carried out by what is known as the light trip method. This is a method in which the mechanism is actuated whenever the light reflective properties of the article integrated over substantially the entire surface thereof exceed a predetermined value. In other words the light trip method is the one in which all lemons lighter than a predetermined standard produce actuation of the mechanism, tripping the lower gate open and enabling such lemons to fall into one receptacle, and all lemons darker than the predetermined standard produce no actuation of the mechanism in consequence of which the lower gate diverts such lemons into another receptacle.

Preferably electronic amplifiers are employed for increasing energy output of the photoelectric tube sufliciently to cause operation of an electromagnet plunger or the like for tripping the lower gate.

Cam mechanism or the equivalent is preferably provided for opening. and closing the upper gate at a predetermined rate and a second cam mechanism or eccentric, or equivalent mechanism, is provided for resetting the lower gate to the closed or divertin position at the same rate. l.'lechani cal drive is provided with gearing of such ratio and so related to the cam and the eccentric that an article progresses to the end of the conveyor and falls upon the upper gate once for each operation of the upper gate, and during the time interval while the upper gate is closed after it has allowed the previous article to fall through the passage in the lamp housing. Likewise, the connections are such as to cause the eccentric to reset the lower gate once for each operation of the upper gate during the interval after an article has fallen through the passage in a lamp housing and while the upper gate is closed.

Although the invention is not limited thereto, preferably I employ a thyratron type of tube, that is a vapor discharge or gaseous discharge amplifier tube, for energizing the tripping magnet of the lower gate which causes it to open upon actuation of the light-responsive mechanism. One or more stages of vacuum tube amplification are interposed between the photoelectric tube and the control electrode or grid of the thyratron tube. A circuit breaking switch or commutator also synchronized with the conveyor, upper gate cam, and the lower gate resetting mechanism is provided in the anode supply circuit of the thyratron tube in order that it may be de-energized after each operation of the lower gate tripping mechanism and be prepared for a subsequent operation.

In order that the point at which the thyratron is tripped in relation to the intensity of the illumination of the photoelectric tube will remain accurately constant and unaffected by various tendencies toward drift, such as aging of the various tubes and filaments, heating of resistors, variations in filament voltage, dust, fingerprints and the like in the lens system and other portions of the optical system, the mechanism is provided with what I call a normalizer. The normalizer serves for intermittently resetting the bias of the operating tube at which it -is neutral with respect to the photoelectric tube.

This is accomplished by providing a condenser coupling between the anode of the vacuum tube amplifier and the control grid of the thyratron,

or between two equivalent points of the circuit,

and resetting the potential on this condenser intermittently and preferably subsequent to each operating cycle of the light trip mechanism.

For the sake of obtaining high precision the condenser is preferably relatively large and for the sake of obtaining high gain the vacuum tube load resistor or anode resistor is preferably relatively large and the vacuum tube is'preferably a pentode tube. Normalization is accomplished by intermittently connecting one side of the normalizing condenser to a point maintained at a predetermined potential. The use of such large condensers and large load resistors, however,

tends to result in a very long time constant preventing complete normalization of the condenser potential difference during the brief interval of time allowed in the short operating cycle corresponding to a high sorting speed and high fre quency of presentation of articles to the photoelectric system. In order to obtain the equivalent of a short-time constant during the normalizing operation, one or more cathode follower tubes are employed. At least one cathode follower tube is employed which is interposed between the last stage vacuum tube amplifier anode and the thyratron control grid so that the charging or discharging current of the condenser during normalization is provided through the cathode follower instead of an anode resistor or other circuit constants. In order to enable a potential-supply of low-current output to be employed for normalizing, a second cathode follower is preferably also provided.

A better understanding of the invention will be afforded by the following detailed description considered in conjunction with the accompanying drawings, inwhich Fig. 1 is a side elevation partially in section of a photoelectric lemon sorter forming an embodiment of the invention;

Fig. 2 is a fragmentary end view of the apparatus of Fig. 1 as seen from the left-hand end;

Fig. 3 is a perspective View of the portion of the apparatus of Fig. 1 including the lamp housmg;

Fig. 4 is a cross-sectional view of the lens housing represented as cut by a horizontal plane 44, indicated in Fig. 1;

Fig. 5 is a vertical mid-section of the portion of the apparatus shown in Fig. 4;

Fig. 6 is a perspective view of the lamp housing employed in the apparatus of Fig. 1;

Fig. '7 is a plan View of the apparatus of Fig. 1;

Fig. 8 is an end elevation partially in crosssection of the apparatus of Fig. 1 as seen from the right-hand end;

Fig. 8A is a fragmentary View of a portion of the apparatus of Fig. 8, showing the lower gate resetting mechanism in another position;

Fig. 9 is a developed view of a drum switch used in the apparatus of Fig. 1;

Fig. 10 is an enlarged, detail plan view of the upper gate of the apparatus shown in Figs, 1 and 7 Fig. 11 is a fragmentary view partially in section of the apparatus of Fig. 10 represented as cut byavertical plane Il--Il;

Fig. 12 is a schematic and circuit diagram of an alternative form of electrical mechanism which may be employed in the apparatus of Figs. 1 to 11;

Fig. 13 is a schematic and circuit diagram of the apparatus of Figs. 1 to 11 employing an optical system such as illustrated in Figs. 3 and 4.

Fig, 14 is a fragmentary view of the uppergate operating mechanism; and

Fig. 15 is a plan view of the lower gate.

Like reference characters are utilized throughout the drawings to designate like parts.

The apparatus shown by way of illustration in Fig. 1 comprises a suitable framework l i supporting a conveyor system I2, shown as being of a progressively moving type such as the screw type with a drive motor and speed-reduction gear unit [3, gearing I l, a timer shaft l5 with associated apparatus to be described in greater detail hereinafter, a lamp housing and viewing r chamber 16, a lens housing 11, a photoelectric tube housing [8, an amplifier case [9 and lemon receptacles 20 and 2|, only one of which is visible in Fig. 1.

As shown more clearly in Fig. 7, the lemon conveyor 12 comprises a pair of horizontal shafts 23 and 24 set close enough together so that the lemons or other articles to be sorted cannot fall through the space between them. One of the shafts 23 has a helical flange or screw 25, formed by a length of large copper tubing wound upon the shaft and secured thereto. oruinariiy the min-a1: pitch (if the helix 2 5 is so chds'n' as to exceed; the maximum expected dimensions or the articles to be sorted,- such as lemons, so that the articles will be: spaced,- as shown in Fig. 7, at distances of the order ohce-and-a-halt or twice their maximum dimensions. Preferably the spiral 25 is graduated so that its: pitch increases along the length of. travel for'oausing the separationbetween articles to increase; The space behind the spiral may befilled in to iorm a spiral groove of substantially constant width. The conveyor shafts 2 3 and 24 extend. from the left-hand: end 26 at which the articles to be sorted are deposited thereon to a: point-above anupper gate 21' provided above the lamp housing I 6;

The' drive mechanism I 4 as i illustrated in Figs. 2' and '7 for the conveyor I 2; comprises a jack shaft 28 carrying a drivepulley 29' and a gear 31 with which are meshed two driven gears or pinions 32 and 33. The pi'nic'ns 32 and 33 are keyed to the conveyor shafts 23' and 24 respectively; There is a belt or chain 34' enabling the pulley 29 to be driven by the motor 1:3, which may include speed reduction gearing, not separately shown. The timer shaft t5 also carries a pulley 35 over which the" belt or chain- 34 passes. The relative diameters of the pulleys 29 and 35 relation to the'relativediameters of the gear 31' and the'pinion 32 an'd 33 are so chosen. that the timer shaft rotates synchronously with the conveyorshaft 23', assuming: a single pitch screw 25'. It is tobe understood: that the arrangement of the mechanism driven by the timer shaft l5 and the conveyor [2 is such that one operation of the mechanism driven by the timer shaft l 5 is obtained for each delivery oi an article, such a ra lemon 36-, from the conveyor I2 to the upper gate 21'.

The lamp housing 161 preferably comprises side walls, illustrated in Fig. 6', formed in the shape of a hexagonal prism, For example, sheet metal maybe bent to shape, as showmwith one or more joints 3-! welde'd or brazed to formaunitary structure; Each or the side walls or faces 38" is provided withan opening 39 to receive an optical device, such as a background screen or a; lightdirectingl object such as a mirror or lens system, as will be described more in detail hereinafter. Annular lam-p pockets or channels M and 42- are joined to the hexagonally formed side walls 38 at their upper and lower edges respectively. The upper wall it of the upper lamp channel 4| is extended inwardly to form the top wall for the lamp housing It with an opening 44 therein at which the upper gate 21' is mounted. Likewise, the lower wall 45 of the lower lampchannel 42 is extended inwardly to form a lower wall for the lamp housing [6 with an opening 46" therein. Lamps ii are mounted in thelamp channels 41 and- 52. In order to shield the falling lemon 36 from the" direct rays of light from any of the lamps il, flanges 50 are provided, as shown in the drawing". There are shields 48 and 49' joined respectively to the upper wall 43 at the edge of the opening 44 and to the lower wall 45 at the edge of the opening 4 6, for equalizing the illumination of the article 36 from various directions, by overcoming excessive light from the ceiling and the floor of the lamp housing.

The lens housing IT i set into one of the side wall openings 39 so as to close the same. As will be explained in the course of further description, the other openings are also closed so that the lamphcusin reform a lightstizht bait,

uppen'edge'ot the shield 4 9ior-msa viewing chamher in which allisidesl of the objects 36 are exposed to the view of a photoelectric cell irrthe cell box r8; without. any necessity for holding the object and without any portion? of the object being obscured by a lamp or by a holder; rest or other support.= The upperopening 44 of the-lamp hous mg It is normally" substantially closed bythe up'per'gate Theloweropenihg 46 is not closed but relatively little light enters" the lamp housing l't' from below.

Instead of a lower closure at the'lower'end of the passageway 44 and 46, a resiliently constructed lower gate diverter, or deflector 51" is provided having a normal position sloping, as shownm Fig. 8-, and adapted to be dropped to a lower or fully opened; position, as represented in Fig. 8A,. which the deflector is substantially vertical. A mm or eccentric mechanism, driven by the timer shaft: f5, as described more fully hereinafter, is provided for operating the upper gate 2 1' and for resetting the: deflector 5i.

The receptacles 2:0: and 21' which may take the form of bins or, the case of fragile articles, flames containing flowing water for floating. the sortedarticles away, are mountedon either: side of the point directly below the lower opening. 46. The receptacle 2i! is so mounted that the" article's falling upon the lower gate or deflector 5| in its normal positionare diverted into the receptacle 20 A- resilient diversion" chute 52' is provided directly below the opening 46 for diverting the falling articlesinto the receptacle 2| when the deflector 51* has been depressed to its fully opened positi'om illustrated in Fig. 8A In this manner the deflector or diverter 51- serves as aselecting mechanism or classifier for classifying articles according to their reflectivity orcolor'and therefore according to the consequent output of the photoelectric mechanism. Preferably the chute 52 is composed of a resilient material, such: as

rubber, plastic or the 1-ike, to avoid: damage to the fallingarticles;

The photoelectric mechanism may be made responsive either to the color or" the reflectivity of the articlefalli-ng through the viewing: chamher" and the lamp housing It. For the' sake of illustration however, the photoelectric mechanism will be described as being of the typeresponsive to reflectivity. It; may be set either for operation upon a reflectivity exceeding a" predetermined value or for operation upon a reflectivity falling below a predetermined value. For the sake of illustration; it is assumed that it is set for what is known as light trip. In this Case the receptacle 20- is the receptacle for dark lemons and the receptacle 2| is the receptacle for light lemons. The timer shaft [5 and the mechanism driven by it are so'set that the upper gate 2-! opens as often as the conveyor I 2 deposits a lemon upon it, but slightly later than this instant. The timer mechanism is also so arranged as to reset the lower gate or' deflector 5i to the position shown in Fig. 8, during the interval after an article has fallen through the lamp chamber I6 and before the upper gate 2! is again opened. Accordingly, if the lemon 36 is lighter than a predetermined value for" which the system is set, the deflector 5| is depressed and the article is an arm 61.

dropped into the light lemon receptacle 2|. On

the other hand, if the lemon is darker than the predetermined value for which the apparatus is set, the gate 5| remains in the position shown in Fig. 8 and deflects the article to the dark receptacle 2B.

, The photoelectric and amplifier apparatus ,for accomplishing the operation of the deflector 5|, according to the light reflectivity of the falling article 35, is represented schematically by a circuit diagram in Fig.13.

i .As illustrated in Figs. 10 and 11, the upper gate 21 comprises a plurality of sector shaped .doors or leaves 53 mounted upon hinges 54 around the periphery of a .oircle coaxial with the lamp housing it at the edges of the hexagonal upper opening 44 of the lamp housing It. As shown by the drawings, the leaves 53 are symmetrical and are symmetrically disposed, so that when the upper gate is closed the leaves slope down inwards toward a center point so as to center each article in a position at the top of its falling path and consequently center the falling path of the articles in the lamp housing. To each sector 53 is secured an operating lever 55, provided at the outer end with a slot 56. For operating the levers 55 in unison, a, ring 5'! is provided which fits in each of the slots 56 and is adapted to be moved upward or downward according to whether the gate 21 is to be opened or closed. For producing such vertical movement of the ring 5?, a pair of arms 58 is provided, which are secured to a shaft 59 and connected to the ring 51 by pintles 6|. For operating the arms 58 a crank 52 is provided carrying a cam follower 63. A cam 54 adapted to engage the cam follower 53, is mounted upon the timer shaft l5. It is to be understood, however, that the invention is not limited to the specific arrangement illustrated and equivalent mechanism may be provided for accomplishing opening and closing of the gate 2? synchronized with the operation of the conveyor l2. Preferably, a spring 65 'is provided for holding the cam follower 63 against the edge of the cam 64.

It will be observed that the upper gate is of 7' the dropping-leaf type. Consequently, when it opens no motion is imparted to the article which has been deposited thereon by the screw conveyor other than the motion produced by the acceleration of gravity. Since the article is already centered, the article falls vertically along a path through the center of the lamp housing. There is no component of horizontal motion. Moreover,

the vertical position of the article in the lamp 1 housing at any instant is accurately related to the instant when the upper gate Was opened by the law expressing the motion of freely falling objects.

The photoelectric sensing apparatus including photoelectric tube means and amplifier means may therefore be rendered sensitive and capable of fast response to light reflected from the article while it is in the viewing position within the lamp housing without requiring that the sensing means be continually sensitive and mechanism for rendering the sensing apparatus sensitive may be driven synchronously with the upper gate operating mechanism.

In order to avoid damage to fragile articles, such as fruit, the deflector 5| is composed of relatively resilient material, such as light, flexible, rubber-coated wire rods for example, each secured at one end to a shaft 56, to which is secured In the arrangement illustrated, the

.side walls in the lamp housing |5.

arm 61 is provided with a spring 68 for depressing the deflector 5| to the lower or fully opened position shown in Fig. 8A. There is a latch 69 for holding the arm 6'! down and the deflector up against the tension of the spring 68. The latch, as illustrated schematically, comprises a sliding bolt formed as an armature or plunger of a solenoid winding 32, adapted to be energized by the amplifier l9 upon response to actuation of the photoelectric cell It for retracting the plunger 1| and tripping the deflector 5|.

For resetting the deflector 5| and the latch 59 after each operation of the solenoid '12 a synchronously moving resetting rod 73 is provided. The rodlS is suitably mounted for axially sliding motion as in a guide M and is arranged to be moved up and down in synchronism with the operation of the upper gate 21, for example. As illustrated, an eccentric or crank arrangement may be provided comprising a, crank disc 15 mounted upon the timer shaft l5 and a connecting rod 78 pivoted at one end to the crank disc E5 by a pin H and at the other end to the upper end of the rod 73. The angular position of the crank pin T! in relation to the dropping portion 78 of the cam 54 is such that the rod 73 is moved downward for resetting the gate 5| 7 slightly before the cam follower 63 is permitted to move to the right under the action of the spring for opening the upper deflector 21. In consequence, the gate 5| is in the reset position shown in Fig. 8, whenever the article 35 falls through the vertical passageway of the light chamber I6. As shown in the drawing the length of the rod 13 is such that its lower end bears against the arm 6'! and depresses it slightly below the catch when the crank pin 11 reaches its lowermost position.

The timer shaft I5 also carries a rotary switch or commutator including a drum l9 cooperating with brushes 8|, 82, 83 and 84. The drum 19, as illustrated in the surface development view of Fig. 9, comprises a cylinder of insulating material 85 into which are set segments of conducting material such as copper segments 86 and 81, having a shape shown in Fig. 9. The arrangement is such that circuit interruptions take place between the brushes 83 and 84 and between the brushes 8| and 82 once for each revolution of the shaft l5, but the circuit interruption between the brushes 83 and 84 takes place while ghe circuit is closed between the contacts SI and The lens housing l1, illustrated in Figs. 3 and 4, comprises a passageway i 55 for direct passage of the light beam intersecting the axis I03 of the lamp housing I6 to a, photoelectric cell or tube 93, which includes a lens system such as an objective lens I66 and a condensing lens lfi'l. In this manner the photoelectric tube 98 and the mechanism controlled thereby are eifectively placed in operative or communicative connection with the interior of the lamp housing l6. As illustrated in the arrangement of Fig. 12, a photoelectric lens system and a corresponding photoelectric tube may also be mounted in the openings 88 and S9 of alternate hexagonally placed Nevertheless, in the embodiment of Fig. 3 and Fig. 13, I have, in order to avoid the use of additional photoelectric tubes and in order to simplify the mechanism, employed mirrors 9| and 92 which are mounted upon suitable supports mounted on base plates for closing the openings 88 and 89. The mirrors 5| and 92 are each mounted at such an angle that light. beams, passing along. the horizontallines intersecting the vertical axis I93 of the lamp housing 16' and impinging upon the mirrors 9| and 92, are reflected. along the axes of passageways 9.3 and 94 in the lenshousing II. The passageways 93 and 94 are also provided with suitable lenses 95. for causing all. three of. the. light beams to be focused at. a. common point. Within the casing I8 for thephotoelectric tube 98. Preferably, transparent. dust covers I.00..are. provided. The remaining three openings 90in. the side walls of the lamp housing I5. have. mounted. therein removable background screens. 91 or reference backgrounds of. the type described; in my Patents. #2,244,826. granted. June 10, 1941. (designated therein by the reference numeral-'30)- and. #2,325,665 granted August 3, 194.6. (designated therein by the reference numeral 46) to serve as standards. of comparison of reflectivity of the articles being sorted. Althoughthelamp. housing has been described. as a. hexagonal prism, it will be understood that my. invention is not limited thereto, as a circular or curved. surface side wall may alsobeemployed with the. reference backgrounds and lightsreceiving and. directing devicesmounted at. approximately the.

same angles, viz. alternately, 60 degrees apart.

InlFig. 4, the circle 310 represents the clearance between light rays along 93-; and 94 andthe directional errors. of an article. falling freely along I03. (Asmaximum: envelope of. paths.)

The photoelectricamplifier, represented in Fig. 13, comprises, in addition. to the photoelectric tube 98,.one or more sensitive amplifier tubes ofthe high vacuum type and. ahigh currrent tube such as.- a gaseous or vapor discharge. tubeof the. thyratron type for energizing. the trip-ping; coil 72... I have. found, however by reason\ of. the improved operation obtained. in accordance. with my invention, that a single. stage of amplification isv ordinarily sufficient and I prefer-- ably employ a single high. vacuum. tube. 99. coupling the photoelectric tube 98 to. athyratron. tube. IIIL. In order that. a single stage of amplification may be employed, a high vacuum. tube 99 is preferably of the pentode type, e. g. a 606 type of tube may be employed, and for the sake of obtaining high amplification a high resistance load is provided for the tube 99 consisting of an. anode resistor I02 which may have a resistance of two megohms, e,.. g. in. the case of use of a 300 volt power supply.

For capacitatively coupling the thyratron Iili' to the pentode 99 a. condenser I09 is provided. The capacity of this condenser is made relatively large. In addition, a bias-fixing connection for the grid of the thyratron. IOI is, in effect, made through what amounts to. infinite resistance during the portion of an operating cycle that the apparatus is functioning for performing a sorting operation or. selection. However, in order that effective bias of the thyratron IIH may be restored to a fixed value and this may be done quickly after each. operation, whatamounts to. very low resistance bias connection is provided. This is accomplished by the employment of a normalizer switch taking the form in the specific apparatus illustrated of the: brushes. B3, B4 and the drum switch segment 81.. The capacity of the condenser I08 is made relatively large because the output terminal is connected to the. grid of tube III where minute grid currents will flow and, through a cable to one of'the normalizing brushes {33 where leakage currents may flow. any such currents cause displacement, of the setting. and. by the, use of large coupling. condensers. the. extent. of the displacement isv reduced. to. a. negligible. quantity. In other words I. aim to obtain, in effect,,the characteristics of a direct-current. amplifier by approaching an. alternatingrcurrent amplifier with infinite time constant. Unavoidaole leaka e currents cause the actual apparatus to falLsomewhat short of. infinite time constant. However, by employing a.cond'enser I08 having a capacity of two microfarads instead ofv .02 microfarad, e..g., the stabilityagainstleaks is. improvedby a factor. of one'hundred.

For the. purpose of. overcoming what would otherwise. be thev long time. constant effect of, the high. pentode. load; resistance I02 and the high capacity I.08;in...a circuit determining the accuracy and rapidity with which the potential of the grid of the thyratron. I0]. is restored to, its predeterminedvalue after each.operation.of the: apparatus, a cathodafollower I09 is interposed betweenthe high potential. plate of. the condenser. I08 and. the anode, of. the pentode. tube 9.9, The. rotary switch brush. 83 is, connected to the. low potential. plate of the. condenser I09 and. the. brush, 8.4 is. connected to a suitable reference voltage which is selected to. bring the grid of. the thyratron to the desired. proximity to the. tripping. point and is the. effective, voltage of the bias. of. the. thyratron I01 determining the trip point. of the thyratron IOI and the solenoid coil I2. The. reference voltage may be the actual critical. voltage, any voltage above which would ignite the thyratron IIlI' when. applied to its control grid. However, thyratronsare ordinarily operated with relatively low trip voltage. It is more practicable to employ a higher reference voltageof the order of 80.volts for example. The use of such a high reference voltage would necessitate a high cathode bias for the thyratron. The thyratron may be so operated; but instead a second cathode follower I II is preferably-interposed between the coupling condenser I03 and the control grid of the thyratron I 0| for, in

7 effect, translating the trip voltage to lower value.

A conventional voltage divider consisting of. resistors. connected in series across the regulated power supply may be employed as. the reference voltage source. In order to avoid the necessity for low-resistance, high-power consumption resistors in the reference voltage source to assure substantially instantaneous normalization, an additionalcathode follower H2 is interposed between the rotary switch brush 84 and a terminal H3 from which the reference voltage is derived. It is to be understood that the invention is. not limited to the use of circuit elements with specific numerical values of electrical constants and specific values and tube types are given merely by way of illustration. However, satisfactory results have been obtained with the pentode 99- taking the form of a 606 tube, the thyratron IN a 2050 tube, the cathode follower tubes I99 being the type 63L? tube and thecathode followers I I I, II 2 twin triode elements of a 6SL7 typeof tube. with a 300' volt power supply; The power supply is represented schematically at H4, but it is to be understood that conventionaltype power pack, preferably regulated, is utilized in practice. Satisfactory operation of the cathode followers I09, III and H2 is obtained with 20,000 ohm resistors connected to the grounded end of the power supply H 4. However, to avoid the necessity for biasing the cathode of the thyratron iIII positively, which ordinarily V 11 trips at approximately minus four volts in the case of a 2050 tube, the cathode of the tube III is preferably connected to a point below ground potential. For this purpose and in order to simplify the circuit arrangement for obtaining light trip operation, a negative power supply I I is also provided which may, for example, be a 300 volt supply.

The cathode follower III is provided with cathode resistance consisting of resistors I I6 and II! in series, the additional resistance provided by the resistor II'I being sufficient to provide additional'voltage drop equaling the voltage of the negative power supply H5. An input connection to the control grid of the thyratron IBI may be taken from a point on the resistor In which may be made adjustable by the use of a sliding tap H8. The tap H8 is set at such a point that the normal potential of the tap H8, With the grid of the cathode follower IlI at the reference voltage, is a suitable value, such as 'minus siX volts for example, in the, case of a I22 in series. The resistors H9, I2! may be con nected directly to the ground if desired, but if the additional resistors I20, I22 are employed, their values are so chosen as to give the same voltage drop as the voltage of the negative source I I5. The resistances of the cathode resistors I I9 and HI represent, such as 20,000 ohms for ex* ample, the effective load resistances of the cathode followers IM and H2.

The reference voltage terminal 9 I3 may be the junction terminal of resistors I23 and IN, con-- nected in series across the power supply ild and having a suitable resistance ratio so as to give the desired reference voltage, e. g. 80 volts. In this case the resistors H6 and H1 may be so chosen as to cause the cathode of the cathode follower tube III to float at 90 volts when the control grid is held at the potential 80 volts,

thereby rendering the voltage of the tap .IIG L,

highly sensitive to rise in voltage of the control grid of the cathode follower III above the predetermined reference voltage, such as 80 volts.

The pentode 99 is provided with suitable dropping resistors I25 and I25 for providing the :3 screen grid potential and preferably also with a cathode resistor I21 for negatively biasing the control grid, especially when no negative power supply is employed. A suitable grid resistor I23 is provided as in conventional circuits.

The amplifier and normalizer circuit of Fig. 13 is described as used in connection with a gravity sorting machine, such as a lemon sorter, which I prefer to operate on alight trip for actuating a lower gate. It is tobe understood, however, that the photoelectric amplifier of Fig. 13 is not lim-' ited in use to the sorting machine herein described by way of illustration and may be also used in numerous other types of photoelectric sorting apparatus where either light or dark trip 'may be desired and where the output of the amplifier represented as the voltage at the point I I9 or at the point 83 may be further amplified before supplying it to a thyratron, or may be supplied directly or through amplification to sweep circuits of a cathode ray tube or in connection ference in connections which will preferably be employed according to whether light trip or dark trip is utilized. If the apparatus is connected for light trip operation the photoelectric tube is provided with a negative potential source through a voltage divider consisting of resistors ISI, I32

and I33 in series connected to the negative terminal of the power supply II5 and to ground through switch contacts I34. For the sake of adjustment the resistor I32 is preferably provided with a sliding tap I35. The photoelectric tube 538 is connected between the tap I35 and the control grid of the pentode 99, preferably in series with the current limiting resistor I35. For light trip the connections are such that the anode it! of the photoelectric tube 98 is connected to the amplifier input through the change-over switch blade I38. Also,.for light trip, the cathode Ifit of the photoelectric tube 98 is connected to the voltage divider tap I35 through the change-over switch blade MI and the resistor I36. Preferably, a smoothing condenser I42 is connected between the ground terminal of the power supply I It and the input terminal of the photoelectric tube. The function of the change-over switch I29 is merely to reverse the connections of the photoelectric tube 98 and to reverse the polarity of the voltage supplied thereto where dark trip is desired instead of light trip.

Where the thyratron IOI is employed, it is pref erably connected to the positive terminal of the power supply H4 through a resistor hi3 shunted by asmoothing condenser I44. Since tubes of the thyratron type remain conductive even after removal of control voltage, an intermittent circuit-opening switch is provided, taking the form in the arrangement illustrated of the brushes ti and 82 cooperating with the contact segment of the drum switch "I9.

In order that the falling object 35, which is to be sorted by the apparatus, will be illuminated on all sides, but only by diffused light, and the photoelectric tube 98 will be affected only by light reflected from the surfaces of the falling object 36 or the reference backgrounds 9?, all of the inner surfaces of the lamp housing It are preferably painted with fiat white lacquer, except the inner surfaces Hi5 of the shields t3 and 43 which are painted with flat black lacquer.

The angular position of the output tip end I46 of the helix 25 of the screw conveyor on the shaft 23, and the angular positions of the cam 8 the crank disc ,55 and the drum switch I9 on the timer shaft I5 relative to each other as interconnected by the gears 32 and 33, the, pulley 35 and the belt or chain 3%, are as indicated in the schematic diagram of Fig. 9.

The lemon or other article L being carried along the conveyor I2 reaches the end of theconveyor above the upper gate 2'5 when the timer shaft I5 and the drum switch iii are in the angular position represented by 300 degreese. g. in

Fig. 9. At this instant both pairs of brushes 8|, 7

mains within the field of view of the photoelectric tube 9% (defined by the lines I58, I59 in Fig. 5) as the timer shaft I5 moves from the angular position 132 to the angular position 168 degrees.

During this time electrical circuit between the brushes '8! and 82 remains closed by the segment I06, but the electrical circuit betweenthe brushes 83 and 84 is open, as they now ride upon the insulatingportion 8-5 of tired-rum 1-9. Accordingly, the condenser itfi is disconnected from the nor-- malizer potential at the cathode of the cathode follower H2.

If the light reflected from the lemon 36 exceeds a predetermined value the resistance of the photoelectric tube 98 falls to such a value as to cause theinput voltage to the pentode 99 to fall below the value at which the potential on the negative plate of the condenser I 68, connected to the brush 83, exceeds thepredetermined reference voltage, e. g. 80 volts, which causes the potential of the thyratron grid to rise above minus four volts and to fire the thyratron WI. Thereupon, current flows through the trip coil l2 retracting the armature 1 i and allowing the spring 68 to lower the gate -51 Accordingly, the lemon 3B falls upon the chute 52 and slides into the light lemon receptacle 2I. "On the other 'hand, if the lemon had been darker than the predetermined value itwou'ldhave fallen upon the lower gate 51 and would have been deflected into the dark lemon receptacle 2!).

During the time subsequent to the interval required for the lemon 36 to fall through the field of view of the photoelectric tube 9'8, the drum switch 19 travels through the angular positions in which the brushes 83 and 84 are in contact throughthe segment 81. The photoelectric tube 98 is-then illuminated only by the light reflected from the reference backgrounds '9-1. The anode potential of the pentode 99 acquires avaluedetermined by the circuit constants, Since the negative plate of the coupling condenser IE8 "is held at the reference voltage, e. g. 80 volts, by the connection to the cathode of the cathode follower IIZ which has its control grid biased at 80 volts, the potential difference between the plates of the condenser I08 is restored, if necessary, to such a value that when the brushes 83 and 84 are again disconnected the potential of the negative plate of the condenser I08 will rise or fall above or below the reference voltage, such "as 80 volts, according to whether illumination ofthe photoelectric tube has been increased'or decreased bypresence of a falling article. Therefore, the apparatus is automatically reset or normalized after each operation so as to respond accurately to the presence of any object having a reflective power greater than the reflective power of the backgrounds 91, as in the light trip operation and vice versa in the caseof dark trip operation.

If any charging current is necessary for correcting the relative potentials on thetwoplates of the coupling condenser M8, i-t-is supplied by in creasing or decreasing the anode-cathode'current flow in thecathode follower tubes I09 and H2, since the current in a cathode-follower automatically increases or decreases whatever amount necessary to cathode potential to follow control grid potential. It is unnecessary for any current to'be drawn through the pentode load resistor I 02 or through the resistors I23 and I24 of the reference voltage source. Consequently, these res-istances do not enter into the time constant of the charging circuit of the condenser I08. The time constant is, in effect, very small for the reason that the effective resistancesof the cathode follower tubes I09 and I 12 are relatively small and, furthermore, it is characteristic of cathode follower tubes that their outputim'pedances, determinati-veof time-constant eflect, are proportional to theratio of load impedance to transconductanee.

The use of a cathode follower tube such as rep resented by tubes I09 and I I2 vastly increases the sensitivity of the sorting apparatus because it permi-ts the use of a pentode amplifier- 99 with a high resistance load H12 in addition .to very high capacity coupling condenser I08. Notwithstanding the large value of electrical constants of the elements 1'02 and I08, the use of the cathode followers 4-09 and I I2 furthermore increases the accuracy of operation by permitting the condenser I08 to be normalized through the switches 83, 84

and I0! very rapidly during the time interval per-' mitted within an operating cycle which must be very small in the case of presentation of articles to be sorted at a high rate of speed. I have found, for example, that an accuracy and stability exceeding .100 times that obtainable without theme of cathode followers have been obtained. The gain in stability is the product of the increase in size of coupling condenser and of the increase in rapidity of normalizing. Inasmuch as the value of automatic sorting depends upon the fineness of decisions which may be made in rejecting or accepting articles deviating but slightly from the background or standard in reflected power, any increase insensitivity is of the utmost importance. Reliable operation of a photoelectric sorting machine in response to a change of one per cent-in illumination of a photoelectric tube has heretofore been possible. However, I have been able to obtain response-reliablyto changes onlyone hundredth as great by use of the arrangement herein described, because :of'a hundred-fold increase in stability.

The increased precision and speed obtained is of particular value in certain locations, such as in tropical countries, e. g. where the difficulty of maintaining insulation and overcoming the effects of moisture is very great and these effects are highly deleteriousowing to producing changes in theteifective resistances of circuit constants and introduction of leakage paths allowing the setting of the apparatus to drift from one operating cycle :to the next, unless the arrangement described herein is employed. Obtaining reliable operation entails consideration not only of the precision obtainable whenthe apparatus is first installed and immediately after adjustment, but also the point at which the apparatus will re spond Without resetting after a period of time. Numerous :factors tend to change the effective setting such as aging of amplifier tubes, variation in filament voltage, imperfect socket connections of lamps and tubes, change in cathode emission, aging of photo tubes, change in resistance of photo .tube load resistors and changes in other resistors, dirt or. fingerprints on lens surfaces, dust on lamp or housing, aging of illuminating lamps, changing. candle power and changes in lamp voltage.

In a multistage amplifier a two-volt drift in a tube results .illgaulrO-Vfilt drift in the next tube if illustrated an arrangement in which a single photoelectric tube 98 is employed in connection with mirrors 9| and 92 for viewing all sides of an object in the gravity sorter, it is to be understood that my invention is not limited thereto. For example, as illustrated in Fig. 12, if desired, three photoelectric tubes 14?, Hit and Hit may be provided, which are mounted. at the side walls the lamp housing It alternate with the positions of the backgrounds at. In this case separate amplifiers Isl, E52 and I53 are provided for each photoelectric tube, arranged for tripping parallel connected thyratrons Hi4, let; and use. The arrangement is such that if any one or the photoelectric tubes 441, [:38 and M9 is illuminated in excess of the standard value (or less in the case of dark trip) one or the other of the thyratrons i54, i523 and IE5 is ignited and current is caused to flow through the tripping coil 112 as in the arrangement of Fig. 13. Once during each operating cycle the anode circuits to all of the thyratrons i5 5, I55 and let are broken by the insulating portion of the drum ls between the brushes 8i and 32.

The hexagonal lamp housing it, or housing with optical elements spaced at 60 degrees or multiples thereof, has the advantage of a high degree of versatility as it may be employed, as shown in Figs. 12 and 13, for obtaining illumination on all sides of an object in the gravity sorter integration of reflectivity of substantially the entire surface or photoelectric response to all sides thereof. In addition, it may be used in connection with point-bypoint or two-dimensional scanning, such as described in my 00- pending' application Serial No. 3,876 filed January 23, 1948, now Patent 2,474,230, granted June 28, 1949. It may, if desired, also be employed in cases Where it is desired or necessary to observe only one side of the object, in which case only one of the photoelectric tubes Hil M8 and I49 and one corresponding amplifier and tripping mechanism need be employed.

While the invention has been described as embodied in concrete form and as operating in a specific manner in accordance with the provisions, of the patent statutes, it should be'understood that the inventionis not limited thereto, since various modifications will suggest themselves to those skilled in the art without departing from the spirit of the invention, the scope of which is set forth in the claims annexed hereto and those presented in my co-pending divisional applications, Serial Number 265,862, filed January 4, 1952, and Serial Number 320,802 filed November 15, 1952.

What I claim is:

.1. In a photoelectric sorter for freely falling articles, an enclosed lamp housing or" the type evenly illuminating an article falling through i the center thereof, having'an upper gate above and selecting mechanism below witha free passage therebetween, for articles to be sorted, shielded from extraneous light, the selecting mechanism being vertically below the upper tionto'the article other than thatcaused by.

theacceleration of gravity, and the upper gate comprising a plurality of symmetrical. symmetrically disposed leaves, sloping down toward a center point when the upper gate is closed for centering articles deposited thereon to provide a uniform path for articles falling through the lamp housing, light responsive means communicatively connected with the lamp housing for actuating the selecting mechanism to shift it from one position to another, and mechanism connected to and synchronous with the upper gate operating mechanism for resetting the selecting mechanism in normal position.

2. In a photoelectric sorter for freely falling articles, a lamp housing having an upper gate with a free passage therebeiow for articles to be sorted, a light responsive means communicating with said lamp housing, a longitudinal conveyor having a delivery end above said gate and including article spacing means of the progressively moving type, gate opening and closing mechanism, article selector mechanism below operatively connected to said light-responsive means and capable of actuation for determining the path of an article below the lamp housing according to the response to light of the article in the lamp housing, and a connected drive for said conveyor and said gate mechanism, with such a speed ratio as to open said gate as frequently as said conveyor advances an amount representing the spacing of said article spacing means, aid upper gate being of the droppingleaf type comprising a plurality of symmetrical, symmetrically disposed leaves, sloping down toward a center point when the upper gate is closed, whereby opening the gate imparts no motion to the article other than that caused by the acceleration or gravity.

3. In a photoelectric sorter, light responsive electric signal producing means including an electronic amplifier of the type having a movable switch therein and capable of being accurately calibrated by movement of the switch to one position and of being rendered sensitive by movement of the switch to another position, an enclosed lamp housing of the type evenly illuminating an object falling through the center thereof, said lamp housing having an upper gate of the dropping leaf type with a passage therebelow through the center of the lamp housing "for objects being sorted, said upper gate comprising a plurality of symmetrical, symmetrically disposed leaves, sloping down toward a center point when the upper gate is closed for centering objects deposited thereon to provide a uniform path for objects falling through the lamp housing, gate opening and closing'mechanism, driving mechanism for synchronously operating saidgate mechanism with said amplifier switch, to hold the switch in position rendering the amplifier sensitive during the period of time that an object is within the lamp housing in consequence of the acceleration of gravity acting thereon during the interval following the instant when the upper gate is opened, and to restore" the switch to calibrating position at other times, and object selecting mechanism below the lamp housing actuated by such signal producing mean according to the reflectivity of objects falling through the lamp housing.

4. A sorting device comprising gate means, a conveyor for depositing objects singly at timed intervals upon the gate means, said gate means having openable leaves sloping down toward a center point for holding each object as deposited thereon by said conveyor and centering it, mechanism rfor opening the leaves downward to release the object held from such a, uniform fixed posi-- tion and to allow the object to fall freely therefrom, a chamber below the gate means with photoelectric means communicating with the chamber for measuring the light reflectivity characteristics of the object while so falling, drive means for said conveyor and said gate opening means, and means for actuating said gate means and said photoelectric means in timed relationship.

5. In a photoelectric sorter for freely falling articles, an enclosed lamp housing of the type evenly illuminating an article falling through the center thereof, having an upper gate above and selecting mechanism below with a free passage therebetween for articles to be sorted, shielded from extraneous light, the selecting mecha nism being vertically below the upper gate and having normal and actuating positions for directing falling articles to one or another of two paths, the upper gate being adapted to have an article deposited thereon when it is in the closed position, and comprising a plurality of symmetrical, symmetrically disposed leaves, each sloping downward toward a center point at one end thereof when the upper gate is closed, for centering articles deposited thereon, each of said leaves being pivoted at the other end thereof with the inner end adapted to drop for opening the gate whereby opening thereof imparts no motion to the article other than that caused by the acceleration of gravity and there is no component of horizontal motion, and light responsive means communicatively connected with the lamp housing for actuating the mechanism to shift it from one position to another for classifying articles deposited upon the upper gate and dropped through the lamp housing.

6. In a sorting machine for fragile articles, a gate for diverting articles not to be accepted, a shaft for supporting said gate pivotally, an arm secured to said shaft, oscillating drive mechanism including a vertically reciprocating member for intermittently bearing against said arm, means for resiliently biasing the arm, a catch 18 for holding said arm against the force of the biasing means slightly above the lowermost position of said reciprocating member, and means responsive to the character of the articles being sorted to release said catch, synchronizing means for causing the release operation to occur only when the reciprocating member is in a position to move said arm away from the catch, whereby the catch may be released without frictional hindrance and the motion of the gate in the event of being released is determined by the motion of said recip rocating member.

DAVID C. COX.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 674,503 Haegg May 21, 1901 781,437 Lelarge Jan. 31, 1905 1,308,053 Gray July 1, 1919 1,394,445 Rogers Oct. 18, 1921 1,677,014 Benford July 10, 1929 1,722,751 Jones July 30, 1929 1,927,217 Price Sept. 19, 1933 1,943,278 Thompson Jan. 9, 1934 1,946,307 Chambers Feb. 6, 1934 1,961,913 Reynolds June 5, 1934 2,035,329 McPhail Mar. 24, 1936 2,131,095 Cox Sept. 27, 1938 2,131,096 Cox Sept. 27, 1938 2,164,513 Gaebel July 4, 1939 2,229,451 Gulliksen Jan. 21, 1941 2,405,483 Abrams Aug. 6, 1945 2,436,762 Turin Feb. 24, 1948 2,444,751 Scott July 6, 1948 2,467,773 Parker Apr. 19, 1949 2,504,731 Rose Apr. 18, 1950 FOREIGN PATENTS Number Country Date 18,035 Great Britain of 1914 294,575 Great Britain Sept. 19, 1928 744,107 France Jan. 21, 1933 492,035 Great Britain Sept. 14, 1938 

